1. Field of the Invention
The present invention relates to a method for molding a synthetic resin structure, a method for molding a pick-up actuator employing the method for molding a synthetic resin structure, a synthetic resin structure molded by the method for molding a synthetic resin structure, and a pick-up actuator molded by the method for molding a pick-up actuator.
2. Description of Related Art
Conventionally, a pick-up actuator is used as a mechanism to record and/or reproduce data to and/or from an optical recording medium. There are a wide variety of pick-up actuators. Recently, among those pick-up actuators, researches are being made into pick-up actuators that can record and/or reproduce data to and/or from an optical recording medium with a higher speed. As an example of such pick-up actuators, there is known a pick-up actuator that has four or more elastic holding members and two or more movable axes (for example, refer to Japanese Patent Laid-Open Publication No. 2001-229555, FIG. 4). The pick-up actuator includes a lens holder that holds an objective lens, a plurality of drive coils, and magnets, and a suspension base that is fixed to an actuator base and swingably holds the lens holder on a plurality of axes using linear elastic members, and that has a skew mechanism that can adjust the angle of the lens holder desirably. The pick-up actuator, which can be reduced in weight and of wider bandwidth, gets a lot of attention.
The pick-up actuator is formed by insert molding, which inserts linear elastic members to a mold for a lens holder and an actuator base, and injects synthetic resin into the mold. In the insert molding, concave cut-off portions may be formed on the surface of respective parts made of synthetic resin so as to equalize thickness thereof, thereby preventing shrinkage of synthetic resin and suppressing strain of linear elastic members (refer to FIG. 18). As shown in FIG. 18, a lens holder 920 is linked to a suspension base 900 through linear elastic members 910. The suspension base 900 and the lens holder 920 are formed by insert molding, which injects synthetic resin into a mold with the linear elastic members 910 placed within the mold. In this case, concave cut-off portions 901 are formed in the suspension base 900. Generally, in injection molding of synthetic resin, in case respective parts are not equalized in thickness without forming such cut-off portions 901, there is undesirably raised shrinkage, that is, recessions are formed on the surface of the respective parts. When shrinkage is raised, pressure is applied to the inserted linear elastic members 910 due to the recessions, which makes the linear elastic members 910 be fixed with its figuration state strained. So as to prevent shrinkage, the suspension base 900 has the concave cut-off portions 901 evenly formed around the linear elastic members 910, which can equalize thickness of respective synthetic resin parts.
The pick-up actuator disclosed in the above-described document is required to have members having various functions built therein together with the lens holder and suspension base, and furthermore, it is desired that the lens holder be reduced in weight to the utmost extent. Accordingly, a pick-up actuator of this type may have its configuration made asymmetric. In this case, the gate position or injection port for injecting synthetic resin at the time of insert molding is arranged in a deviated position. Thus, at the time of injection molding, some points of the linear elastic members are strongly affected by flow of synthetic resin, while some points of the linear elastic members are weakly affected by flow of synthetic resin, depending on the distance from the gate position. As a result, points of the linear elastic members which are strongly affected by flow of synthetic resin are strained due to pressure brought about by the flow of synthetic resin, and raise angular difference as compared with points of the linear elastic members which are weakly affected by flow of synthetic resin.
Furthermore, when the cut-off portions are not formed on the surface, recessions may be formed on the suspension base due to shrinkage, which may strain the linear elastic members.
Moreover, since the cut-off portions 901 have their dimensions equalized, in case the gate position is arranged in a deviated position, forming the cut-off portions 901 on the surface as shown in FIG. 18 does not solve the above-described affection by flow of synthetic resin.
When the linear elastic members are strained, the relative angle of the lens holder and the suspension base of the pick-up actuator (angle due to rotation around the X-axis and the Y-axis shown in FIG. 18) become large, which undesirably increases skew adjustment range. Thus, height dimension of the actuator becomes large, which undesirably leads to disadvantage in providing a small-sized lightweight device.
Furthermore, when recording and/or reproducing data to and/or from an optical recording medium, the pick-up actuator follows the displacement of the optical recording medium substantially in the vertical direction (focusing direction) as well as substantially in the horizontal direction (tracking direction) along the recording surface thereof. At this time, when the linear elastic members are strained, large skews may be raised due to strokes along the focusing direction and tracking direction, which undesirably lowers recording and/or reproducing capabilities. Especially, strain of linear elastic members, which is admissible in an optical recording medium of comparatively low density and low capacity such as a conventionally known CD (Compact disc) or DVD (Digital versatile disc), cannot be ignored when using an optical recording medium of high density and high capacity such as a recently remarkable Blue-ray disc.